This invention relates to a method of correcting an analytical value of a plasma or serum sample obtained by filtering blood using a glass fiber filter.
The type or concentration of blood components, such as metabolites, proteins, lipids, electrolytes, enzymes, antigens, and antibodies, is measured, in general, using a plasma or serum sample obtained by centrifuging whole blood. However, centrifuging takes labor and time. Particularly, centrifuging is unsuitable for an urgent case of measuring a small number of samples promptly and in site inspection, because of requiring a centrifuge and electricity. Thereupon, it has been investigated to separate serum from whole blood by filtration.
Several filtration methods using glass fiber filters have been developed wherein whole blood is charged into the glass fiber put in a column from one side of the column, and pressurized or evacuated to obtain plasma or serum from the other side (Japanese Patent KOKOKU Nos. 44-14673, 5-52463, Japanese Patent KOKAI Nos. 2-208565, 4-208856).
However, practical filtration methods capable of obtaining an amount of plasma or serum from whole blood necessary for measuring by an automatic analyzer have not been developed except a part of items, such as blood sugar.
On the other hand, the inventors developed a blood filter cartridge composed of a filter holder and a syringe. The filter holder is composed of a holder body which contains filter material and a cap which is screwed on the holder body. The filter material consists of, e.g. two sheets of glass fiber filter, one sheet of cellulose filter and one sheet of polysulfone microporous membrane (FIG. 1 of EP 785430 A1).
Another blood filter cartridge composed of a holder body and a cap was also developed. The holder body consists of a plasma receiver located on the upper side and a filter chamber located on the underside. The filter material put in the filter chamber is composed of six sheets of glass fiber filter and one sheet of polysulfone microporous membrane (Example 1 of EP 785012A1).
Incidentally, the electrolytes to be measured for clinical assay include calcium, sodium, potassium, chlorine and so on. However, as a result of investigating commercial glass fiber filters, the inventors found that some of them are eluted into blood to cause analytical errors.
They also found that analytical errors were caused by proteins, ammonia formed nitrogen, and enzymes, such as alkaline phosphatase.
An object of the invention is to provide an analytical method capable of removing an error caused by the filtration of blood using a glass fiber filter, and thereby to provide a simple method of analyzing a blood component.
The inventors investigated eagerly in order to solve the above problems, and found that, the errors caused by a glass fiber filter due to electrolytes, proteins, ammonia formed nitrogen, enzymes and the like are represented by a linear equation, and the errors generated by the same type of glass fiber filters are almost equal. Accordingly, the errors can be corrected by the linear equation of which two factors have previously been determined as to the analytical item to be measured.
The present invention has been made based on the above findings, and provides a method of analyzing a blood component by filtering blood using a glass fiber filter to obtain a plasma or serum sample and measuring the sample, wherein some plasma or serum samples obtained by using the same type glass fiber filter and by a standard method have previously been measured to determine a and b of the formula
Y=ax+b
wherein Y is the analytical value obtained by the standard method and x is the analytical value obtained by using the glass fiber filter, and the analytical value of the blood is corrected by using the above formula.